The role of intraspecific hybridization in the evolution of invasiveness: a case study of the ornamental pear tree Pyrus calleryana

Hybridization between genetically distinct populations of a single species can serve as an important stimulus for the evolution of invasiveness. Such intraspecific hybridization was examined in Pyrus calleryana, a Chinese tree species commonly planted as an ornamental in residential and commercial areas throughout the United States. This self-incompatible species is now escaping cultivation and appearing in disturbed habitats, where it has the potential to form dense thickets. Using genetic techniques incorporating nine microsatellite markers, we show that abundant fruit set on cultivated trees as well as the subsequent appearance of wild individuals result from crossing between genetically distinct horticultural cultivars of the same species that originated from different areas of China. We conclude that intraspecific hybridization can be a potent but little recognized process impacting the evolution of invasiveness in certain species.     

Flavonoid genes of pear (<Emphasis Type="Italic">Pyrus communis</Emphasis>)

Pear (Pyrus sp.) is a major fruit crop of temperate regions with increasing extent of cultivation. Pear flavonoids contribute to its fruit color, pathogen defense, and are health beneficial ingredients of the fruits. Comparative Southern analyses with apple (Malus x domestica) cDNAs showed comparable genomic organization of flavonoid genes of both related genera. A homology-based cloning approach was used to obtain the cDNAs of most enzymes of the main flavonoid pathway of Pyrus: phenylalanine ammonia lyase, chalcone synthase, chalcone isomerase, flavanone 3β-hydroxylase, flavonol synthase, dihydroflavonol 4-reductase, leucoanthocyanidin reductase 1 and 2, anthocyanidin synthase, anthocyanidin reductase, and UDP-glucose : flavonoid 7-O-glucosyltransferase. The substrate specificities of the recombinant enzymes expressed in yeast were determined for physiological and non-physiological substrates and found to be in general agreement with the characteristic pear flavonoid metabolite pattern of mainly B-ring dihydroxylated anthocyanins, flavonols, catechins, and flavanones. Furthermore, significant differences in substrate specificities and gene copy numbers in comparison to Malus were identified. Cloning of the cDNAs and studying the enzymes of the Pyrus flavonoid pathway is an essential task toward a comprehensive knowledge of Pyrus polyphenol metabolism. It also elucidates evolutionary patterns of flavonoid/polyphenol pathways in the Rosaceae, which allocate several important crop plants.     

Identification and characterization of Colletotrichum species associated with anthracnose on persimmon in Brazil

Persimmon (Diospyros kaki) anthracnose is a major threat in production areas worldwide. Most of the studies are focused on Colletotrichum horii, but other species have been reported as well. The association of distinct Colletotrichum species present in Brazilian persimmon production regions as well as their host ranges are yet elusive. The aims of this work were to identify and characterize Colletotrichum species associated with the persimmon anthracnose. In a survey performed in four production regions of Brazil, 88.7% and 11.3% out of 231 isolates were identified as members of Colletotrichum gloeosporioides species complex (Cgc) or Colletotrichum acutatum species complex (Cac), respectively. A subset of 18 isolates were identified through multilocus phylogenetic analysis, using ITS-rDNA region and two loci, namely GAPDH and TUB2. This study revealed the presence of four species: C. horii (38.8%) and Colletotrichum fructicola (27.7%) from the Cgc and Colletotrichum nymphaeae (27.7%) and Colletotrichum melonis (5.8%), from the Cac. Additionally, 13 isolates were selected for morphological, physiological, and pathogenic analyses. Contrasting characteristics were observed among species of the Cgc and Cac complexes. The optimal temperature for mycelial growth and germination were higher for Cgc species. The percentage of appressoria melanisation also varied across complexes. All the identified species were able to cause anthracnose-like symptoms on persimmon fruit, leaves, shoots, and sepals. Colletotrichum species from persimmon were also able to infect apple and pear. The findings will support decisions to manage anthracnose of persimmon under high infection risk due to multiple host susceptibility.     

梨种质资源主要描述标准比较分析

介绍了国内外6个梨种质资源描述标准,并对其主要形态特征与农艺性状描述符进行了归纳整理;分析了各描述符标准的层次结构特征、生物胁迫与非生物胁迫评价内容以及描述符编码方式;指出了制定我国梨相关标准借鉴之处.     

Alleviation of frost damage to pear flowers by application of gibberellin

Adverse effects of gibberellin applications on pear trees after frost such as small fruit size, abnormal fruit shape and poor return bloom are often attributed both to the sole use of GA₃ and its overdose. It is unclear whether protection against spring frosts before flower opening is more efficient when GA is applied directly after frost, i.e. before flower opening, or at full bloom or both. In April 2003, early spring frosts at Klein-Altendorf near Bonn, Germany damaged ca. 88% flowers of the early flowering cv. Alexander Lucas, 64% of cv. Conference and ca. 25% of flowers of the later flowering cv. Comice pears. Hence, the objective of the present work was to investigate the optimum timing of the application of low doses of the combined GA₃ and GA_{4 + 7} to improve parthenocarpic fruit set in pears, while maximising fruit quality and size for trees affected by a severe spring frost before full bloom. Return bloom was also considered and quantified. Frost-affected pear trees were treated with gibberellin GA₃+GA_{4 + 7}, either immediately after the frost, at the white bud stage, or at full bloom or both to improve parthenocarpic set. Early flowering cv. Alexander Lucas pear was most affected by the early spring frost, but lost only 25% of fruitlets at June drop, irrespective of GA treatment. June drop was, however, severe in the two other cultivars least affected by frost, i.e. by 33% in cv. Conference and 55% in cv. Comice. Both initial and final fruit set were significantly increased by a combined application of GA₃+GA_{4 + 7} at full bloom, without affecting return bloom, but June drop was also enhanced by GA application. The largest positive effect of GA application on fruit yield, an additional 2 kg of fruit per tree equivalent to €1200/ha, was apparent with the cv. Alexander Lucas, i.e. the cultivar most affected by frost. There was no loss in fruit quality viz fruit size after any of the GA applications with any of the pear cultivars examined and no increase in abnormally-shaped, elongated fruit.     

梨锈病病菌生态位研究

安徽主栽梨树品种对锈病菌的抗性差异显著,而对感病品种以病情指数和病叶数为依据的锈菌寄主生态位进行研究,结果生态位宽度依次是０．７５５５和０．７９５１;各品种水平空间和垂直空间生态位宽度均接近于１。此研究表明梨锈病菌是以随机扩散传播侵染的。     

PCR detection of MLOs in quick decline-affected pear trees in Italy

Polymerase chain reaction (PCR) amplification, using primers derived from the 16S rRNA gene, followed by restriction fragment length polymorphism (RFLP) analysis with Alu I restriction endonuclease was used to detect myc-oplasma-like organisms (MLOs) associated with pear decline. MLOs were consistently detected in pear trees that suddenly wilted and died within a few days during summer, as well as in pears of the same orchards with symptoms similar to the slow form of pear decline. In both cases the same RFLP pattern was obtained. Declining pear trees were 5 to 8-yr-old cvs Williams, Kaiser and Max Red Bartlett grafted on to Pyrus communis seedling rootstocks. All the orchards affected by quick decline had severe attacks of pear psyllid (Cacopsylla pyri) during the year this study was performed and during the previous year. The results showed the suitability of DNA amplification by the polymerase chain reaction for the detection of pear decline MLOs and established that MLOs can be detected in infected tissues of dead trees.     

梨不同DNA提取方法的效果研究

以7个梨品种为实验材料,比较分析了SDS法、CTAB法、SDSCTAB法、改良的CTAB法、高盐低pH值法、分步离心法对梨总DNA提取的效果。结果表明:利用以上6种方法提取的梨总DNA在纯度和量上有很大的差别。所得到的平均DNA量从大到小依次为:分步离心法、SDS法、SDSCTAB法、改良的CTAB法、CTAB法、高盐低pH值法。DNA提取纯度依次为分步离心法、SDSCTAB法、改良的CTAB法、高盐低pH值法、CTAB法、SDS法。RAPD和自交不亲和基因(S基因)特异性引物扩增实验结果都比较理想,但分步离心法和SDSCTAB法提取的DNA双酶切效果较好。分步离心法提取的梨总DNA更适用于后续的分子生物学实验操作。     

Correlation between population size of pear Psylla (Cacopsylla chinensis) and leaf structure features in different pear cultivars

The feeding preference of pear psylla (Cacopsylla chinensis) varies among pear cultivars. To clarify whether leaf structural factors are related to C. chinensis resistance, eleven pear cultivars of three pear species and their hybrids in China were studied. The population size of C. chinensis in plots of different cultivars was investigated, and leaf paraffin sections of each pear cultivar were observed. Correlation analysis results showed that the thickness of palisade tissue (PT) and the thickness ratio (TR) of PT to leaf (L) were the main factors influencing resistance to C. chinensis. The leaves of cultivar Wujiuxiang and those species from France and the USA exhibited the thickest PT and the highest TR; these three cultivars demonstrated much higher resistance to C. chinensis than did the other cultivars. The cultivar Gold Nijisseiki, with a large C. chinensis population size, showed low PT and TR. The findings of this study may provide valuable information to pear growers, experts and scientists regarding plant protection, cultivation and breeding when selecting suitable varieties to culture from the perspective of pest control.     

Effectiveness of second mating for two incompatible types of the citrus red mite,Panonychus citri (McGregor)

Two types of the citrus red mite, Panonychus citri (M.) occur in some pear orchards in the intermediate latitudal areas in Japan during a certain period of the year (Takafuji andMorimoto , 1983): one is a diapausing type ( DP ) and the other a non-diapausing type ( C ). These two types are incompatible: no adult females are produced from the crosses between them (Takafuji andFujimoto , 1985). In the present study, females of each type were doubly crossed, first with a male of the other type, and then with a male of the same type, to examine the effectiveness of the second mating. In the females of the DP type, the second mating with a male of the same type was almost totally ineffective. In contrast, for the females of the C type the effectiveness of the second mating depended on the durations of the first and second matings: the famles produced female offspring only when the duration of the first copulation with a male of the DP type was brief and the second copulation with a male of the C type lasted relatively long. The results suggested that if the two types coexist, the intercrossing between them will favour the C type over the DP type.